1. Field of the Invention
The present invention relates to a sliding member structure which is used for, for example, a lens barrel and in which one member and another member slidably move relative to each other, and a manufacturing method of the same.
2. Description of the Related Art
Hitherto, as a structure in which one member and another member slidably move relative to each other, for example, there have been known a helicoid structure including a male helicoid (male screw) and a female helicoid (female screw), a structure including a ball screw and a nut, and a structure including a fixed barrel and a movable barrel as extension-type lens barrels. The helicoid structure is a mechanism for converting rotational movement to linear movement. The male helicoid is configured by forming a single or a plurality of screw threads in a trapezoidal or triangular cross-sectional shape along a helical path determined in advance. The helical path is determined depending on a movement distance (lead) in a rotational axis direction for a rotational degree. The female helicoid is provided with screw grooves screwed together with the screw threads of the male helicoid.
The helicoid structure is used for an optical system for moving a lens in an optical axis direction in an optical device such as a projection-type projector or a camera. For example, when the helicoid structure is used for a barrel of a camera, an inner barrel (helicoid member) having a male helicoid on its outer periphery and an outer barrel (helicoid member) having a female helicoid screwed together with the male helicoid on its inner periphery are provided, and one barrel is moved relative to the other barrel in the optical axis direction by rotating the barrels relative to each other. The helicoid members using this kind of helicoid structure are generally manufactured by injection molding using synthetic resin materials which are advantageous in terms of low cost and mass production.
Since the screw threads and screw grooves of the helicoid members have small pitches and have complex shapes, when they are manufactured by injection molding, contraction, shrinkage, or the like occurs. When a large degree of contraction or shrinkage occurs, dimensional precision is degraded, and rattling may occur between the male and female helicoids. When rattling occurs in an optical device which applies the helicoid structure and has a configuration in which, for example, a focus lens group and remaining lens groups are moved relative to each other, optical characteristics may be deteriorated.
Here, for helicoid members disclosed in JP-A-2005-83568, a lubricating material such as grease is applied to a clearance between male and female helicoids to suppress rattling. In addition, for the helicoid members disclosed in JP-A-2005-83568, with regard to a plurality of screw threads or screw grooves of at least one of the male and female helicoids, a single screw thread or screw groove is not provided to increase the clearance between the male and female helicoids and insert the lubricating material into the clearance.
In addition, two-color molding for forming only contact surfaces of the male and female helicoids using a soft resin material such as an elastomer and forming other parts thereof using a hard resin material so as to allow the male and female helicoids to come in close contact with each other during screwing is considered. Otherwise, pressing the male and female helicoids against each other using a biasing member such as a spring to suppress rattling is considered.
However, in the helicoid members disclosed in JP-A-2005-83568, properties including hardness and viscosity of the lubricating material such as grease vary due to environmental temperature or circumstances. Therefore, when the helicoid structure is operated, due to relative positions of the male and female helicoids or positions of the center of gravity of the helicoids, points with slight rattling and points with considerable rattling coexist, so that the helicoid structure cannot be stably operated.
In addition, in the configuration in which the helicoid members are allowed to come in close contact with each other by the biasing member, the helicoid members can be relatively easily pressed against each other in the axis direction. However, structurally, it is difficult to press the helicoid members against each other in a radial direction along the entire periphery, and the number of components and processes to assemble the biasing member is further increased, resulting in an increase in cost.
In addition, in the method of manufacturing the helicoid members using the two-color molding in which only the contact surfaces or the vicinity thereof of the male and female helicoids are made of the soft resin, a shrinkage ratio is high, and dimensional precision is degraded. Furthermore, when one helicoid member of the male and female helicoids is subjected to two-color molding and the other helicoid member is subjected to one-color molding, a combination of resins having different shrinkage ratios is produced. Therefore, in order to screw the two helicoid members together with good precision by controlling molding shrinkage, a number of tests need to be performed, which results in an increase in cost.